1. Field of the Invention
The present invention relates to a pressure-sensitive adhesive tape for use in various types of fastening such as fastening of hygienic goods such as diapers, fixing of cloths, binding of various articles, etc. and more particularly to a pressure-sensitive adhesive tape having two or more different pressure-sensitive adhesive layers. The present invention also relates to a pressure-sensitive adhesive tape for disposable diapers using such a type of pressure-sensitive adhesive tape and to a disposable diaper having such a pressure-sensitive adhesive tape. Furthermore, the present invention relates to a structure for attaching a fastening tape comprising a pressure-sensitive adhesive tape with two or more different pressure-sensitive adhesive layers together with a release tape to a disposable diaper.
2. Description of the Related Art
Various persons including babies and young infants generally use hygienic goods such as disposable diapers. Hygienic goods use a pressure-sensitive adhesive tape as one of constituent materials. In the case of disposable diapers, pressure-sensitive adhesive tapes are used to fasten the diaper to the wearer or compacting and disposing the diaper after its use.
In the case of disposable diapers, one end of the fastening tape is applied to the rear portion of the chassis (back body) of a diaper. Application of the other end of the fastening tape to a frontal tape fixed to the front portion of the chassis (front body) of diaper makes the disposable diaper to be fastened to the body of a wearer. After its use, peeling off the other end of the fastening tape from the frontal tape releases the fixing of the disposable diaper to the body of wearer. On the pressure-sensitive adhesive layer of the other end of the pressure-sensitive adhesive tape, usually a release tape is temporarily applied in order to protect the pressure-sensitive adhesive layer until its use. In other words, disposable diapers each comprise a plurality of tapes, for example, a fastening tape for fixing the disposable diaper to the body of a wearer, a release tape, a frontal tape for releasably applying the fastening tape.
For example, JP-A-10-168399 (JP-A means unexamined published patent application) discloses pressure-sensitive adhesive sheets comprising a substrate with two pressure-sensitive adhesive layers, one pressure-sensitive adhesive layer is a pressure-sensitive adhesive layer which is non-adhesive or slightly adhesive at room temperature composed mainly of a polymer having a specified polycarbonate structure and showing a peeling power between pressure-sensitive adhesive surfaces being 100 to 2000 g/20 mm width initially and after 24 hours, and the other pressure-sensitive adhesive layer composed mainly of a polymer which is different from the polymer constituting the one pressure-sensitive adhesive layer. JP-A-5-247419 discloses a structure of a peeling portion whose interface is constituted by a pressure-sensitive adhesive layer and a release coated layer, in which the pressure-sensitive adhesive layer comprises a rubber- or acrylic-based pressure-sensitive adhesive composition and has a 100% modulus measured under the following tensile test conditions is 1.5 kg/cm2 or less in the case of the rubber-based pressure-sensitive adhesive composition or 1.0 kg/cm2 or less in the case of the acrylic-based pressure-sensitive adhesive composition:
Measurement Conditions:
(1) Test piece Thickness 200xc2x110 xcexcm, cross-section 1 mm2; length of specimen between grips 10 mm;
(2) Measurement conditions: Temperature: 20xc2x0 C., elongation rate: 50 mm/min.
Recently, higher quality disposable diapers are being developed and it is a trend to try to switch the material of disposable diapers to nonwoven fabrics, which have less stimulation to the skin of the wearer, are soft to the skin, have good touch and give a high grade sense.
However, nonwoven fabrics are porous and difficult to secure sufficient adhesion area as compared with plastic films. Therefore, when in use as a back sheet of a disposable diaper, the fastening tape cannot cope with the shearing force applied on the fastening tape so that the fastening tape cannot be sufficiently adhered and fixed to the back sheet. As shown in FIG. 8, which is a schematic cross-sectional view showing a conventional structure for attaching fastening and release tapes to the chassis of a disposable diaper, it has been contemplated to reinforce the adhesion and fixing of a fastening tape X and a release tape W to a pressure-sensitive adhesive layer 2 on a pressure-sensitive adhesive tape backing 1 and a pressure-sensitive adhesive layer 8 on a pressure-sensitive adhesive tape substrate 1B, respectively, by overlapping the pressure-sensitive adhesive layers 2 and 8 by about 5 mm to contact each other. However, this involves a partially superimposed structure, which gives hard touch upon use. On the other hand, if the adhesive strength of the adhesive layer is increased too much, the applied fastening tape itself sometimes tends to peel off the surface of the back sheet. This is the case particularly when fastening tapes of the type which can decrease peeling sounds are selected. Therefore, pressure-sensitive adhesive tapes are being desired, which overcomes the problems of decreasing peeling sounds generated when the adhesion between the fastening tape and frontal tape is released and of realizing strong adhesion and fixing therebetween.
Under the circumstances, the present invention has been made.
An object of the present invention is to provide a pressure-sensitive adhesive tape having strong adhesion to a back-sheet of a disposal diaper, etc. and an appropriate re-releasing function from a frontal tape, etc.
Furthermore, another object of the present invention is to provide a pressure-sensitive adhesive tape which can suppress generation of peeling sounds, which is uncomfortable, upon releasing the fastening tape from the frontal tape. Still another object of the present invention is to provide a pressure-sensitive adhesive tape for disposable diapers using such a type of pressure-sensitive adhesive tape.
Yet another object of the present invention is to provide a disposable diaper having such a pressure-sensitive adhesive tape.
Furthermore, an object of the present invention is to provide a structure for attaching a fastening tape comprising a pressure-sensitive adhesive tape with two or more different pressure-sensitive adhesive layers and a release tape to a disposable diaper.
The present inventors have made extensive research with view to obviate the above problems and as a result they have found that provision of at least two different kinds of pressure-sensitive adhesive layers on the substrate of a pressure-sensitive adhesive tape and setting the moduli at 50% elongation and 200% elongation of the pressure-sensitive adhesives constituting the respective pressure-sensitive adhesive layers to specified values can give rise to a pressure-sensitive adhesive tape having strong adhesion and fixation to a back-sheet comprising nonwoven fabric and at the same time decrease peeling sounds upon releasing the fastening tape from the frontal tape. The present invention has been achieved based on this discovery.
That is, the pressure-sensitive adhesive tape of the present invention comprises a substrate having thereon at least two different kinds of pressure-sensitive adhesive layers, wherein one pressure-sensitive adhesive layer (A) is constituted by a pressure-sensitive adhesive having a modulus at 50% elongation of 68, 650 to 117, 680 Pa and a modulus at 200% elongation of 147,100 to 245,170 Pa and another pressure-sensitive adhesive layer (B) is constituted by a pressure-sensitive adhesive having a modulus at 50% elongation of 19, 610 to 68,650 Pa and a modulus at 200% elongation of 68,650 to 147,100 Pa.
Here, the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer (A) may comprise a pressure-sensitive adhesive comprising 100 parts by weight of styrene block copolymer, 5 to 30 parts by weight of a softener which is liquid at a normal temperature (23xc2x0 C.), 110 to 200 parts by weight of a tackifier which is solid at a normal temperature (23xc2x0 C.) and the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer (B) may comprise 100 parts by weight of styrene block copolymer, 20 to 50 parts by weight of a softener which is liquid at a normal temperature, and 60 to 105 parts by weight of a tackifier which is solid at a normal temperature (23xc2x0 C.).
The adherend on which the pressure-sensitive adhesive layer (A) is adhered may be non-woven fabric.
The pressure-sensitive adhesive layers (A) and (B) may have a gap of 0.1 to 15 mm therebetween.
Any of the above pressure-sensitive adhesives may be used in disposable diapers.
The disposable diaper of the present invention comprises any of the above pressure-sensitive adhesive tape.
In another embodiment, the disposable diaper of the present invention comprises a fastening tape and a release tape, wherein the fastening tape comprises any of the above pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer (A), which is adhered and fixed to a back-sheet of the chassis of the disposable diaper and wherein the release tape having on one surface a pressure-sensitive adhesive layer is fixed to the chassis of the disposable diaper with the pressure-sensitive adhesive layer of the release tape being not in contact with the fastening tape, and wherein another pressure-sensitive layer (B) of the fastening tape is able to be releasably attached to the opposite surface of the release tape.
The structure for attaching a tape to the chassis of a disposable diaper according to the present invention is a structure for attaching a fastening tape and a release tape to the chassis of a disposable diaper, wherein the fastening tape comprises any of the above tapes and the pressure-sensitive adhesive layer of the fastening tape and the pressure-sensitive adhesive layer of the release tape do not contact each other.
The pressure-sensitive adhesive tape of the present invention comprises a backing and two or more different pressure-sensitive adhesive layers on one surface of the backing. For example, it exhibits excellent effects on an adherend having a portion which adheres strongly and a portion which adheres releasably, such as the fastening tape in a disposable diaper. However, its use is not limited to disposable diapers and may be effectively used where an adherend consisting of two or more materials is to be fixed or in some other cases.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments with reference to the attached drawings.